Field of the Invention
The present invention relates to a laser machining apparatus for laser-machining a workpiece such as a semiconductor wafer.
Description of the Related Art
In a semiconductor device manufacturing process, the surface of an approximately disk-shaped semiconductor wafer is partitioned into a plurality of areas by scheduled division lines that are formed in a grid pattern, with a device such as IC or LSI formed in each of the partitioned areas. Then, a semiconductor wafer is cut along scheduled division lines, thus dividing the wafer into areas, each having a device formed therein and manufacturing individual device chips. An optical device wafer having light-receiving elements such as photodiodes or light-emitting elements such as laser diodes stacked on the surface of a sapphire substrate is similarly cut along scheduled division lines, thus dividing the wafer into individual optical devices such as photodiodes or laser diodes for application to a wide range of electronic equipment.
In order to divide a wafer such as semiconductor wafer or optical device wafer along scheduled division lines as described above, a method has been proposed which forms laser-machined grooves by irradiating a pulsed laser beam at a wavelength that is absorbed by the wafer along scheduled division lines and breaking the wafer along the scheduled division lines where the laser-machined grooves are formed. A laser machining apparatus for performing such laser machining includes chuck table, laser beam irradiation means, and machining feed means. The chuck table holds a workpiece. The laser beam irradiation means laser-machines the workpiece held by the chuck table. The machining feed means moves the chuck table and the laser beam irradiation means relatively in the machining feed direction. Then, the laser beam irradiation means includes laser beam oscillation means and a condenser. The laser beam oscillation means oscillates a laser beam. The condenser includes a condenser lens adapted to collect the laser beam oscillated by the laser beam oscillation means and irradiate the beam onto the workpiece held by the chuck table.
Further, a laser machining apparatus has been proposed which permits two kinds of laser machining by splitting a pulsed laser beam, oscillated by laser beam oscillation means, into two paths using a polarization beam splitter (for example, Japanese Patent Laid-Open No. 2008-114239).